Open Office

Open Office, originally developed as Star Writer (1985, by Star Division) and upgraded to Star Office (1999, by Sun Microsystems), is a modular program package containing usual office tools. A spin-off happened in 2010 to produce Libre Office.

Given that the full suite is free, this is one of the best deals you'll find in all of computing. It'll do just about anything you expect from an office suite, whether creating documents, spreadsheets, or presentations. You'll find solid formatting tools, as well as extras including mail merge, macros, charting capabilities, and more.

There are many extensions available for each module of the office suite. In context with eReader devices two options are remarkable:

Writer2ePub is an extension that can generate a fully functional ePub directly from within Writer.

As a regular part of the suite all modules can export customized PDF files directly.

PerfectEpub is an extension that allows you to find and fix, in text files, a large amount of formatting errors resulting from incorrect formatting when writing, scans or conversions of formats, such as PDF.